Alternating-phase-focused IH-DTL for an injector of heavy-ion medical accelerators

A compact Drift-Tube-Linac (DTL) using an Interdigital H-mode (IH) cavity was designed for an injector of medical accelerators. For beam focusing, the method of Alternating-Phase-Focusing (APF) was applied. The APF IH-DTL can accelerate heavy ions having a charge-to-mass ratio of q/m=13 up to 4.0MeV/u. Having optimized an array of synchronous phases for cells, namely arranging drift tubes and gaps appropriately, both longitudinal and transverse focusing strengths were produced just with the rf acceleration field, and therefore no focusing element or cooling equipments had to be installed in the cavity. This allowed us to employ a rather high operating frequency, and hence to design a compact and cost-effective cavity. A further advantage of the APF linac can be found in its operation. Since the parameters to be adjusted are just the level and phase of the input rf, beam tuning can be made with ease. Consequently, the APF linac is suitable for an injector for medical accelerators. Tuning methods of the gap voltages and cavity frequency as well as the design of the cavity for APF IH-DTL have been developed. After constructing the cavity, measurements of the electric field and tuning of the gap voltages were performed. Finally, the rf power was fed into the cavity. In this paper, the design and results of the measurements are described.